Inorganic fine particles such as metal oxide powders have been conventionally used for electrophoto-graphic developers to improve fluidity. Further, there have been made many proposals with regard to the control of the charge quantities (i.e., the tribocharges) of the developers, which have an influence on developability. When charge control is made by an external additive, inorganic fine particle whose surface has been treated with a positive or negative surface treating agent has been conventionally added to a toner. For example, a fine silica particle having a negative chargeability is treated with an amino group-containing silane coupling agent to obtain an electrophotographic developer having a positive chargeability. Further, there have been proposed fine metal oxide particles whose surfaces are treated with 5 to 20% by weight of an amino group-containing silane coupling agent as well as 5 to 20% by weight of a hydrophobizing agent (i.e., agent giving a hydrophobic property) to impart a hydrophobic property to the developer, each amount being based on the weight of the fine metal oxide particle [see, JP-A-58-185405 (the term "JP-A" as used herein means an "unexamined published Japanese patent application")].
Further, an electrophotographic developer having a positive chargeability comprising a toner composition containing a binder resin and a colorant, and a silica fine particle which is vapor phase-oxidized with a silicon halogen compound is described in JP-B-1-40979 (the term "JP-B" as used herein means an "examined Japanese patent publication").
Chargeability and charge quantity can be controlled by inorganic fine particles conventionally proposed. However, the mixing of the toner (toner admixability) with the developer is not sufficiently made during toner supply, and a toner having a wide charge distribution is formed. Accordingly, there are conventionally problems that developing apparatuses are stained, or background stain on the copied image is formed. There has been not found a technique as yet, which enables the charge control of the toner as well as the improvement of the toner admixability to be simultaneously made. This invention has been performed with a view to solve the above-mentioned problems.